MMP9 and COVID-19: MMPs are able to break-down excreted proteins like collagen and elastin fibers of the extracellular matrix (ECM) [10], are necessary for ECM restructuring, wound recovery, and vessel formation, and a number of them, such as MMP-1 and MMP-9, have been found to play a role in the immunopathogenesis of interstitial pulmonary fibrosis (IPF) [[11], [12], [13], [14]], a condition which is associated with COVID-19 [15] and other conditions [16].